This project is an investigation of the reasons for resistance during certain times in their growth cycle of some malignant cell lines in continuous culture to the normally cytotoxic effects of antibody to membrane antigens and complement. Expression of membrane antigens, interaction with antibody and the nature and extent of interaction of complement components are to be quantitated. Demonstrated complement dependent changes in membrane structure are to be examined as a tool for determination of the possibility of membrane repair. Oncogenic viruses and other viruses which bud from the cell membrane will be examined for mechanism of interaction with complement and it will be determined whether the phenomenon of activation of the alternative complement pathway with ensuing lysis of the infected cells is a general phenomenon.